Implant delivery system

ABSTRACT

A system and method of delivering and detaching an implant within a body of a patient is described. A tether connects an implant with a delivery device. The delivery device includes a heater coil through which the tether passes. The inner diameter of the heater coil is about the same size or slightly larger than the outer diameter of the tether, allowing the tether to more efficiently break the tether during delivery.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/169,629, filed Apr. 15, 2009 entitled Implant Delivery System, whosecontents are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to systems and methods for deliveringimplant devices to a target site or location within the body of apatient. The present invention also relates to a method of detectingimplant detachment within the body of a patient.

BACKGROUND OF THE INVENTION

Delivery of implantable therapeutic devices by less invasive means hasbeen demonstrated to be desirable in numerous clinical situations. Forexample, vascular embolization has been used to control vascularbleeding, to occlude the blood supply to tumors, to occlude fallopiantubes, and to occlude vascular aneurysms, particularly intracranialaneurysms. In recent years, vascular embolization for the treatment ofaneurysms has received much attention. Implants used to treat aneurysmsare often convoluted or coiled lengths of wound wire and are referred toas “microcoils.” Microcoils work by filling an aneurysm causing theblood flow through the aneurysm to slow or stop, thereby inducingthrombosis within the aneurysm.

Microcoils are extremely flexible and have very little structuralintegrity. In order to make them easier to retrieve and reposition,recent efforts have been directed to making them stretch-resistant. Forexample, a stretch-resistant embolic coil having a stretch-resistantmember passing through the interior lumen of the coil is described inU.S. Pat. No. 5,582,619 to Ken. US Patent Publication No. 2004/0034363to Wilson also discloses an embolic coil with a stretch resistant memberhaving a distal end attached near the distal end of the coil and aproximal end of the member attached to a delivery catheter.

Several different treatment modalities have been employed in the priorart for deploying implant devices. For example, numerous repositionabledetachment systems for implant devices have been described in the priorart including U.S. Pat. No. 5,895,385 to Guglielmi et al. and U.S. Pat.No. 5,108,407 to Geremia et al., the contents of which are herebyincorporated by reference. Several systems, such as those disclosed inU.S. Pat. No. 6,500,149 to Gandhi et al. and U.S. Pat. No. 4,346,712 toHanda et al., the contents of which are hereby incorporated byreference, describe the use of a heater to detach and deploy the implantdevice.

While implant delivery and detachment systems are known in the art, theydo not provide the user feedback that the implant has indeed detachedfrom the delivery device. This is especially important in cases wherethe detachment relies on the application of heat or an electrolyticprocess where an element of time is involved. These delivery devicesleave the user in the position of wondering whether heat etc., has beenapplied long enough to cause detachment. Hence, there exists a need fora method of detecting whether an implant has properly and effectivelydetached within the body of a patient.

SUMMARY OF THE INVENTION

The present invention is an implant delivery and detachment system usedto position and deploy implantable devices such as coils, stents,filters, and the like within a body cavity including, but not limitedto, blood vessels, fallopian tubes, malformations such as fistula andaneurysms, heart defects (e.g. left atrial appendages and sepalopenings), and other luminal organs.

The system comprises an implant, a delivery catheter (genericallyreferred to as the pusher or delivery pusher), a detachable joint forcoupling the implant to the pusher, a heat generating apparatus(generically referred to as the heater), and a power source to applyenergy to the heater.

The present invention also includes a method for detecting detachment ofan implant. In particular, detachment of an implant is detected bymeasuring the change in the electrical resistance of the deliverysystem.

The present invention may also be used in conjunction with the deliverymechanism disclosed in U.S. patent application Ser. No. 11/212,830 filedAug. 25, 2005 entitled “Thermal detachment system for implantingdevices,” which is incorporated by reference herein in its entirety.

In one aspect of the present invention, the implant is coupled to thepusher using a tether, string, thread, wire, filament, fiber, or thelike. Generically this is referred to as the tether. The tether may bein the form of a monofilament, rod, ribbon, hollow tube, or the like.Many materials can be used to detachably join the implant to the pusher.One class of materials is polymers such as polyolefin, polyolefinelastomer such as those made by Dow marketed under the trade name Engageor Exxon marketed under the trade name Affinity, polyethylene, polyester(PET), polyamide (Nylon), polyurethane, polypropylene, block copolymersuch as PEBAX or Hytrel, and ethylene vinyl alcohol (EVA); or rubberymaterials such as silicone, latex, and Kraton. In some cases, thepolymer may also be cross-linked with radiation to manipulate itstensile strength and melt temperature. Another class of materials ismetals such as nickel titanium alloy (Nitinol), gold, and steel. Theselection of the material depends on the capacity of the material tostore potential energy, the melting or softening temperature, the powerused for detachment, and the body treatment site. The tether may bejoined to the implant and/or the pusher by welding, knot tying,soldering, adhesive bonding, or other means known in the art. In oneembodiment where the implant is a coil, the tether may run through theinside lumen of the coil and be attached to the distal end of the coil.This design not only joins the implant to the pusher, but also impartsstretch resistance to the coil without the use of a secondary stretchresistant member. In other embodiments where the implant is a coil,stent, or filter; the tether is attached to the proximal end of theimplant.

In another aspect of the present invention, the tether detachablycoupling the implant to the pusher acts as a reservoir of stored (i.e.potential) energy that is released during detachment. Thisadvantageously lowers the time and energy required to detach the implantbecause it allows the tether to be severed by application of heatwithout necessarily fully melting the material. The stored energy alsomay exert a force on the implant that pushes it away from the deliverycatheter. This separation tends to make the system more reliable becauseit may prevent the tether from re-solidifying and holding the implantafter detachment. Stored energy may be imparted in several ways. In oneembodiment, a spring is disposed between the implant and pusher. Thespring is compressed when the implant is attached to the pusher byjoining one end of the tether to one of either the pusher or implant,pulling the free end of the tether until the spring is at leastpartially compressed, then affixing the free end of the tether to theother of the implant or the pusher. Since both ends of the tether arerestrained, potential energy in the form of tension on the tether (orcompression in the spring) is stored within the system. In anotherembodiment, one end of the tether is fixed as in the previousembodiment, and then the tether is placed in tension by pulling on thefree end of the tether with a pre-determined force or displacement. Whenthe free end of the tether is then affixed, the elongation (i.e. elasticdeformation) of the tether material itself stores energy.

In another aspect of the present invention, a heater is disposed on orwithin the pusher, typically, but not necessarily, near the distal endof the pusher. The heater may be attached to the pusher by, for example,soldering, welding, adhesive bonding, mechanical boding, or othertechniques known in the art. The heater may be in the form of a woundcoil, heat pipe, hollow tube, band, hypotube, solid bar, toroid, orsimilar shape. The heater may be made from a variety of materials suchas steel, chromium cobalt alloy, platinum, silver, gold, tantalum,tungsten, mangalin, chromium nickel alloy available from California FineWire Company under the trade name Stable Ohm, conductive polymer, or thelike. The tether is disposed in proximity to the heater. The tether maypass through the lumen of a hollow or coil-type heater or may be wrappedaround the heater. Although the tether may be disposed in direct contactwith the heater, this is not necessary. For ease of assembly, the tethermay be disposed be in proximity to, but not actually touching, theheater.

The delivery catheter or pusher is an elongate member with distal andproximal ends adapted to allow the implant to be maneuvered to thetreatment site. The pusher comprises a core mandrel and one or moreelectrical leads to supply power to the heater. The pusher may taper indimension and/or stiffness along the length, with the distal end usuallybeing more flexible than the proximal end. In one embodiment, the pusheris adapted to be telescopically disposed within a delivery conduit suchas a guide catheter or microcatheter. In another embodiment, the pushercontains an inner lumen allowing it to be maneuvered over a guide wire.In still another embodiment, the pusher can be maneuvered directly tothe treatment site without a secondary device. The pusher may have aradiopaque marking system visible with fluoroscopy that allows it to beused in conjunction with radiopaque markings on the microcatheter orother adjunctive devices.

In another aspect of the present invention, the core mandrel is in theform of a solid or hollow shaft, wire, tube, hypotube, coil, ribbon, orcombination thereof. The core mandrel may be made from plastic materialssuch as PEEK, acrylic, polyamide, polyimide, Teflon, acrylic, polyester,block copolymer such as PEBAX, or the like. The plastic member(s) may beselectively stiffened along the length with reinforcing fibers or wiresmade from metal, glass, carbon fiber, braid, coils, or the like.Alternatively, or in combination with plastic components, metallicmaterials such as stainless steel, tungsten, chromium cobalt alloy,silver, copper, gold, platinum, titanium, nickel titanium alloy(Nitinol), and the like may be used to form the core mandrel.Alternatively, or in combination with plastic and/or metalliccomponents, ceramic components such as glass, optical fiber, zirconium,or the like may be used to form the core mandrel. The core mandrel mayalso be a composite of materials. In one embodiment, the core mandrelcomprises an inner core of radiopaque material such as platinum ortantalum and an outer covering of kink-resistant material such as steelor chromium cobalt. By selectively varying the thickness of the innercore, radiopaque identifiers can be provided on the pusher without usingsecondary markers. In another embodiment, a core material, for examplestainless steel, with desirable material properties such as kinkresistance and/or compressive strength is selectively covered (by, forexample, plating, drawing, or similar methods known in the art) with alow electrical resistance material such as copper, aluminum, gold, orsilver to enhance its electrical conductivity, thus allowing the coremandrel to be used as an electrical conductor. In another embodiment, acore material, for example, glass or optical fiber, with desirableproperties such as compatibility with Magnetic Resonance Imaging (MRI),is covered with a plastic material such as PEBAX or polyimide to preventthe glass from fracturing or kinking.

In another aspect of the present invention, the heater is attached tothe pusher, and then one or more electrical conductors are attached tothe heater. In one embodiment a pair of conductive wires runsubstantially the length of the pusher and are coupled to the heaternear the distal end of the pusher and to electrical connectors near theproximal end of the pusher. In another embodiment, one conductive wireruns the substantially the length of the pusher and the core mandrelitself is made from a conductive material or coated with a conductivematerial to act as a second electrical lead. The wire and the mandrelare coupled to the heater near the distal end and to one or moreconnectors near the proximal end of the pusher. In another embodiment, abipolar conductor is coupled to the heater and is used in conjunctionwith radiofrequency (RF) energy to power the heater. In any of theembodiments, the conductor(s) may run in parallel to the core mandrel ormay pass through the inner lumen of a substantially hollow core mandrel(for example, a hypotube).

In another aspect of the present invention, an electrical and/orthermally insulating cover or sleeve may be placed over the heater. Thesleeve may be made from insulating materials such as polyester (PET),Teflon, block copolymer, silicone, polyimide, polyamide, and the like.

In another aspect of the present invention, electrical connector(s) aredisposed near the proximal end of the pusher so that the heater can beelectrically connected to a power source through the conductors. In oneembodiment, the connectors are in the form of a plug with one or moremale or female pins. In another embodiment, the connector(s) are tubes,pins, or foil that can be connected with clip-type connectors. Inanother embodiment, the connector(s) are tubes, pins, or foil that areadapted to mate with an external power supply.

In another aspect of the present invention, the pusher connects to anexternal power source so that the heater is electrically coupled to thepower source. The power source may be from battery(s) or connected tothe electrical grid by a wall outlet. The power source supplies currentin the form of direct current (DC), alternating current (AC), modulateddirect current, or radiofrequency (RF) at either high or low frequency.The power source may be a control box that operates outside of thesterile field or may be a hand-held device adapted to operate within asterile field. The power source may be disposable, rechargeable, or maybe reusable with disposable or rechargeable battery(s).

In another aspect of the present invention, the power source maycomprise an electronic circuit that assists the user with detachment. Inone embodiment, the circuit detects detachment of the implant andprovides a signal to the user when detachment has occurred. In anotherembodiment, the circuit comprises a timer that provides a signal to theuser when a pre-set length of time has elapsed. In another embodiment,the circuit monitors the number of detachments and provides a signal orperforms an operation such as locking the system off when a pre-setnumber of detachments have been performed. In another embodiment, thecircuit comprises a feedback loop that monitors the number of attachmentattempts and increases the current, voltage, and/or detachment time inorder to increase the likelihood of a successful detachment.

In another aspect of the present invention, the construction of thesystem allows for extremely short detachment time. In one embodiment thedetachment time is less than 1 second.

In another aspect of the present invention, the construction of thesystem minimizes the surface temperature of the device duringdetachment. In one embodiment, the surface temperature at the heaterduring detachment is under 50° C. In another embodiment, the surfacetemperature at the heater during detachment is under 42° C.

In another aspect of the present invention, detachment of the implant isdetected by measuring a change in the electrical resistance of thedelivery system, specifically the heater zone, to detect implantdetachment.

These and other aspects and features of the present invention will beappreciated upon consideration of the following drawings and detaileddescriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional side view of a first embodiment ofa detachment system according to the present invention;

FIG. 2 illustrates a cross-sectional side view of a second embodiment ofa detachment system according to the present invention;

FIG. 3A illustrates example direct signaling current according to thepresent invention;

FIG. 3B illustrates example alternating signaling current according tothe present invention;

FIG. 4 illustrates a cross-sectional side view of a third embodiment ofa detachment system according to the present invention;

FIG. 5 illustrates example temperature data of the surface of adetachment system according to the present invention;

FIG. 6 illustrates a cross-sectional side view of an electricalconnector of a detachment system according to the present invention;

FIG. 7 illustrates a cross-sectional side view of radiopaque layers of adetachment system according to the present invention; and

FIG. 8 illustrates a cross-sectional side view of a detachment systemincluding a stent according to the present invention;

FIG. 9 illustrates a side view of a implant device according to thepresent invention;

FIG. 10 illustrates a perspective view of a coil and spacer of thedelivery system of FIG. 9;

FIG. 11 illustrates a side view of a pusher of the delivery system ofaccording to the present invention;

FIG. 12 illustrates a side view of the pusher of the delivery system ofFIG. 11;

FIG. 13 illustrates a perspective view of a delivery system according tothe present invention;

FIG. 14 illustrates a side view of the delivery system of FIG. 13;

FIG. 15 illustrates a perspective view of the delivery system of FIG.13;

FIG. 16 illustrates a side view of the tether and implant device of FIG.13;

FIG. 17 illustrates a side view of the delivery system of FIG. 13; and

FIG. 18 illustrates a side view of an alternate tether arrangement forthe delivery system of FIG. 13.

DETAILED DESCRIPTION OF THE INVENTION

Turning to FIG. 1, a detachment system 100 of the present invention, andspecifically the distal portion of the detachment system 100, isillustrated. The detachment system 100 includes a pusher 102 that ispreferably flexible. The pusher 102 is configured for use in advancingan implant device 112 into and within the body of a patient and,specifically, into a target cavity site for implantation and delivery ofthe implant device 112. Potential target cavity sites include but arenot limited to blood vessels and vascular sites (e.g., aneurysms andfistula), heart openings and defects (e.g., the left atrial appendage),and other luminal organs (e.g., fallopian tubes).

A stretch-resistant tether 104 detachably couples the implant 112 to thepusher 102. In this example, the tether 104 is a plastic tube that isbonded to the pusher 102. A substantially solid cylinder could also be adesign choice for the tether 104. The stretch resistant tether 104extends at least partially through the interior lumen of an implantdevice 112.

Near the distal end of the pusher 102, a heater 106 is disposed inproximity to the stretch resistant tether 104. The heater 106 may bewrapped around the stretch resistant tether 104 such that the heater 106is exposed to or otherwise in direct contact with the blood or theenvironment, or alternatively may be insulated by a sleeve, jacket,epoxy, adhesive, or the like. The pusher 102 comprises a pair ofelectrical wires, positive electrical wire 108 and negative electricalwire 110. The wires 108 and 110 are coupled to the heater 106 by anysuitable means, such as, e.g., by welding or soldering.

The electrical wires 108, 110 are capable of being coupled to a sourceof electrical power (not shown). As illustrated the negative electricalwire 110 is coupled to the distal end of the heater 106 and the positiveelectrical wire 108 is coupled to the proximal end of the heater 106. Inanother embodiment, this configuration may be reversed, i.e., thenegative electrical wire 110 is coupled to the proximal end of theheater 106 while the positive electrical wire 108 is coupled to thedistal end of the heater 106.

Energy is applied to the heater 106 from the electrical wires 108, 110in order to sever the portion of the tether 104 in the proximity of theheater 106. It is not necessary for the heater 106 to be in directcontact with the tether 104. The heater 106 merely should be insufficient proximity to the tether 104 so that heat generated by theheater 106 causes the tether 104 to sever. As a result of activating theheater 106, the section of the stretch resistant tether 104 that isapproximately distal from the heater 106 and within the lumen of animplant device 112 is released from the pusher 102 along with theimplant device 112.

As illustrated, the implant device 112 is an embolic coil. An emboliccoil suitable for use as the implant device 112 may comprise a suitablelength of wire formed into a helical microcoil. The coil may be formedfrom a biocompatible material including platinum, rhodium, palladium,rhenium, tungsten, gold, silver, tantalum, and various alloys of thesemetals, as well as various surgical grade stainless steels. Specificmaterials include the platinum/tungsten alloy known as Platinum 479 (92%Pt, 8% W, available from Sigmund Cohn, of Mount Vernon, N.Y.) andnickel/titanium alloys (such as the nickel/titanium alloy known asNitinol).

Another material that may be advantageous for forming the coil is abimetallic wire comprising a highly elastic metal with a highlyradiopaque metal. Such a bimetallic wire would also be resistant topermanent deformation. An example of such a bimetallic wire is a productcomprising a Nitinol outer layer and an inner core of pure referencegrade platinum, available from Sigmund Cohn, of Mount Vernon, N.Y., andAnomet Products, of Shrewsbury, Mass.

Commonly-assigned U.S. Pat. No. 6,605,101 provides a further descriptionof embolic coils suitable for use as the implant device 112, includingcoils with primary and secondary configurations wherein the secondaryconfiguration minimizes the degree of undesired compaction of the coilafter deployment. The disclosure of U.S. Pat. No. 6,605,101 is fullyincorporated herein by reference. Furthermore, the implant device 112may optionally be coated or covered with a hydrogel or a bioactivecoating known in the art.

The coil-type implant device 112 resists unwinding because the stretchresistant tether 104 that extends through the lumen of the implantdevice 112 requires substantially more force to plastically deform thanthe implant device 112 itself. The stretch resistant tether 104therefore assists in preventing the implant device 112 from unwinding insituations in which the implant device 112 would otherwise unwind.

During assembly, potential energy may be stored within the device tofacilitate detachment. In one embodiment, an optional spring 116 isplaced between the heater 106 and the implant device 112. The spring iscompressed during assembly and the distal end of the tether 104 may betied or coupled to the distal end of the implant device 112, or may bemelted or otherwise formed into an atraumatic distal end 114.

In one embodiment, the stretch resistant tether 104 is made from amaterial such as a polyolefin elastomer, polyethylene, or polypropylene.One end of the tether 104 is attached to the pusher 102 and the free endof the tether 104 is pulled through the implant 112 with the proximalend of the implant 112 flush to either the heater 106 (if no spring 116is present) or to the compressed spring 116. A pre-set force ordisplacement is used to pre-tension the tether 104, thus storing energyin an axial orientation (i.e. co-linear or parallel to the long axis ofthe pusher 102) within the tether 104. The force or displacement dependson the tether material properties, the length of the tether 104 (whichitself depends on the tether's attachment point on the pusher and thelength of the implant). Generally, the force is below the elastic limitof the tether material, but sufficient to cause the tether to severquickly when heat is applied. In one preferred embodiment wherein theimplant to be deployed is a cerebral coil, the tether has a diameterwithin the range of approximately 0.001 to 0.007 inches. Of course thesize of the tether can be changed to accommodate different types andsizes of other implants as necessary.

Turning to FIG. 2, another embodiment of a detachment system of thepresent invention, detachment system 200, is illustrated. Detachmentsystem 200 shares several common elements with detachment system 100.For example, the same devices usable as the implant device 112 withdetachment system 100 are also usable as the implant device 112 withdetachment system 200. These include, e.g., various embolic microcoilsand coils. The implant device 112 has been previously described withrespect to detachment system 100. As with the implant device 112, thesame identification numbers are used to identify otherelements/components of detachment system 100 that may correspond toelements/components of detachment system 200. Reference is made to thedescription of these elements in the description of detachment system100 as that description also applies to these common elements indetachment system 200.

With detachment system 200, an interior heating element 206 is used toseparate a section of a stretch resistant tube 104 and an associatedimplant device 112 from the detachment system 200. Detachment system 200includes a delivery pusher 202 that incorporates a core mandrel 218. Thedetachment system 200 further includes a positive electrical wire 208and a negative electrical wire 210 that extend through the lumen of thedelivery pusher 202.

To form the internal heating element 206, the positive electrical wire208 and the negative electrical wire 210 may be coupled to the coremandrel 218 of the delivery pusher 202. Preferably, the electrical wires208, 210 are coupled to a distal portion of the core mandrel 218.

In one embodiment, the positive electrical wire 208 is coupled to afirst distal location on the core wire 218, and the negative electricalwire 210 is coupled to a second distal location on the core wire 218,with the second distal location being proximal to the first distallocation. In another embodiment, the configuration is reversed, i.e.,the positive electrical wire 208 is coupled to the second distallocation and the negative electrical wire 210 is coupled to the firstdistal location on the core wire 218. When the positive electrical wire208 and the negative electrical wire 210 are coupled to the distalportion of the core mandrel 218, the distal portion of the core mandrel218 along with the electrical wires 208, 210 forms a circuit that is theinterior heating element 206.

The heater 206 increases in temperature when a current is applied from apower source (not shown) that is coupled to the positive electrical wire208 and the negative electrical wire 210. If a greater increase intemperature/higher degree of heat is required or desired, a relativelyhigh resistance material such as platinum or tungsten may be coupled tothe distal end of the core mandrel 218 to increase the resistance of thecore mandrel 218. As a result, higher temperature increases are producedwhen a current is applied to the heater 206 than would be produced witha lower resistance material. The additional relatively high resistancematerial coupled to the distal end of the core mandrel 218 may take anysuitable form, such as, e.g., a solid wire, a coil, or any other shapeor material as described above.

Because the heater 206 is located within the lumen of the tube-shapedtether 104, the heater 206 is insulated from the body of the patient. Asa result, the possibility of inadvertent damage to the surrounding bodytissue due to the heating of the heater 206 may be reduced.

When a current is applied to the heater 206 formed by the core mandrel218, the positive electrical wire 208, and the negative electrical wire210, the heater 206 increases in temperature. As a result, the portionof the stretch resistant tether 104 in proximity to the heater 206severs and is detached, along with the implant device 112 that iscoupled to the tether 104, from the detachment system 200.

In one embodiment of the detachment system 200, the proximal end of thestretch resistant tether 104 (or the distal end of a larger tube (notshown) coupled to the proximal end of the stretch resistant tether 104)may be flared in order to address size constraints and facilitate theassembly of the detachment system 200.

In a similar manner as with detachment system 100, energy may be storedwithin the system with, for example, an optional compressive spring 116or by pre-tensioning the tether 104 during assembly as previouslydescribed. When present, the release of potential energy stored in thesystem operates to apply additional pressure to separate the implantdevice 112, and the portion of the stretch resistant tether 104 to whichthe implant device 112 is coupled, away from the heater 206 when theimplant device 112 is deployed. This advantageously lowers the requireddetachment time and temperature by causing the tether 104 to sever andbreak.

As with detachment system 100, the distal end of the stretch resistanttether 104 of detachment system 200 may be tied or coupled to the distalend of the implant device 112, or may be melted or otherwise formed intoan atraumatic distal end 114.

FIG. 4 illustrates another preferred embodiment of a detachment system300. In many respects, the detachment system 300 is similar to thedetachment system 200 shown in FIG. 2 and detachment system 100 shown inFIG. 1. For example, the detachment system 300 includes a deliverypusher 301 containing a heater 306 that detaches an implant device 302.Detachment system 300 also utilizes a tether 310 to couple the implantdevice 302 to the delivery pusher 301.

In the cross-sectional view of FIG. 4, a distal end of the deliverypusher 301 is seen to have a coil-shaped heater 306 that is electricallycoupled to electrical wires 308 and 309. These wires 308, 309 aredisposed within the delivery pusher 301, exiting at a proximal end ofthe delivery pusher 301 and coupling to a power supply (not shown). Thetether 310 is disposed in proximity to the heater 306, having a proximalend fixed within the delivery pusher 301 and a distal end coupled to theimplant device 302. As current is applied through wires 308 and 309, theheater 306 increases in temperature until the tether 310 breaks,releasing the implant device 302.

To reduce the transfer of heat from the heater 306 to the surroundingtissue of the patient and to provide electrical insulation, aninsulating cover 304 is included around at least the distal end of theouter surface of the delivery pusher 301. As the thickness of the cover304 increases, the thermal insulating properties also increase. However,increased thickness also brings increased stiffness and a greaterdiameter to the delivery pusher 301 that could increase the difficultyof performing a delivery procedure. Thus, the cover 304 is designed witha thickness that provides sufficient thermal insulating propertieswithout overly increasing its stiffness.

To enhance attachment of the tether 310 to the implant device 302, theimplant device 302 may include a collar member 322 welded to the implantdevice 302 at weld 318 and sized to fit within the outer reinforcedcircumference 312 of the delivery pusher 301. The tether 310 ties aroundthe proximal end of the implant device 302 to form knot 316. Furtherreinforcement is provided by an adhesive 314 that is disposed around theknot 316 to prevent untying or otherwise unwanted decoupling.

In a similar manner as with detachment systems 100 and 200, energy maybe stored within the system with, for example, an optional compressivespring (similar to compressive spring 116 in FIG. 1 but not shown inFIG. 4) or by axially pre-tensioning the tether 104 during assembly. Inthis embodiment, one end of the tether 310 is attached near the proximalend of the implant device 302 as previously described. The free end ofthe tether 310 is threaded through a distal portion of the deliverypusher 301 until it reaches an exit point (not shown) of the deliverypusher 301. Tension is applied to the tether 310 in order to storeenergy in the form of elastic deformation within the tether material by,for example, placing a pre-determined force on the free end of thetether 310 or moving the taut tether 310 a pre-determined displacement.The free end of the tether 310 is then joined to the delivery pusher 301by, for example, tying a knot, applying adhesive, or similar methodsknown in the art.

When present, the release of potential energy stored in the systemoperates to apply additional pressure to separate the implant device302, and the portion of the tether 310 to which the implant device 302is coupled, away from the heater 306 when the implant device 302 isdeployed. This advantageously lowers the required detachment time andtemperature by causing the tether 310 to sever and break.

The present invention also provides for methods of using detachmentsystems such as detachment systems 100, 200, or 300. The followingexample relates to the use of detachment system 100, 200, or 300 foroccluding cerebral aneurysms. It will, however, be appreciated thatmodifying the dimensions of the detachment system 100, 200, or 300 andthe component parts thereof and/or modifying the implant device 112, 302configuration will allow the detachment system 100, 200, or 300 to beused to treat a variety of other malformations within a body.

With this particular example, the delivery pusher 102, 202, or 301 ofthe detachment system 100, 200, or 300 may be approximately 0.010 inchesto 0.030 inches in diameter. The tether 104, 310 that is coupled nearthe distal end of the delivery pusher 102, 202, or 301 and is coupled tothe implant device 112, 302 may be 0.0002 inches to 0.020 inches indiameter. The implant device 112, 302; which may be a coil, may beapproximately 0.005 inches to 0.020 inches in diameter and may be woundfrom 0.0005 inch to 0.005 inch wire.

If potential energy is stored within the detachment system 100, 200, or300, the force used to separate the implant device 112, 302 typicallyranges up to 250 grams.

The delivery pusher 102, 202, or 301 may comprise a core mandrel 218 andat least one electrically conductive wire 108, 110, 208, 210, 308, or309. The core mandrel 218 may be used as an electrical conductor, or apair of conductive wires may be used, or a bipolar wire may be used aspreviously described.

Although the detachment systems 100, 200, and 300 have been illustratedas delivering a coil, other implant devices are contemplated in thepresent invention. For example, FIG. 8 illustrates the detachment system300 as previously described in FIG. 4 having an implant that is a stent390. This stent 390 could similarly be detached by a similar method aspreviously described in regards to the detachment systems 100, 200, and300. In a further example, the detachment systems 100, 200, or 300 maybe used to deliver a filter, mesh, scaffolding or other medical implantsuitable for delivery within a patient.

FIG. 7 presents an embodiment of a delivery pusher 350, which could beused in any of the embodiments as delivery pusher 102, 202, or 301,which includes radiopaque materials to communicate the position of thedelivery pusher 350 to the user. Specifically, the radiopaque markermaterial is integrated into the delivery pusher 350 and varied inthickness at a desired location, facilitating easier and more precisemanufacturing of the final delivery pusher 350.

Prior delivery pusher designs, such as those seen in U.S. Pat. No.5,895,385 to Guglielmi, rely on high-density material such as gold,tantalum, tungsten, or platinum in the form of an annular band or coil.The radiopaque marker is then bonded to other, less dense materials,such as stainless steel, to differentiate the radiopaque section. Sincethe radiopaque marker is a separate element placed at a specifieddistance (often about 3 cm) from the tip of the delivery pusher, theplacement must be exact or the distal tip of the delivery pusher 350 canresult in damage to the aneurysm or other complications. For example,the delivery pusher 350 may be overextended from the microcatheter topuncture an aneurysm. Additionally, the manufacturing process to make aprior delivery pusher can be difficult and expensive, especially whenbonding dissimilar materials.

The radiopaque system of the present invention overcomes thesedisadvantages by integrating a first radiopaque material into most ofthe delivery pusher 350 while varying the thickness of a secondradiopaque material, thus eliminating the need to bond multiple sectionstogether. As seen in FIG. 7, the delivery pusher 350 comprises a coremandrel 354 (i.e. the first radiopaque material), preferably made fromradiopaque material such as tungsten, tantalum, platinum, or gold (asopposed to the mostly radiolucent materials of the prior art designssuch as steel, Nitinol, and Elgiloy).

The delivery pusher 350 also includes a second, outer layer 352, havinga different radiopaque level. Preferably, outer layer 352 is composed ofa material having a lower radiopaque value than the core mandrel 354,such as Elgiloy, Nitinol, or stainless steel (commercially availablefrom Fort Wayne Metals under the trade name DFT). In this respect, boththe core mandrel 354 and the outer layer 352 are visible anddistinguishable from each other under fluoroscopy. The outer layer 352varies in thickness along the length of the delivery pusher 350 toprovide increased flexibility and differentiation in radio-density. Thusthe thicker regions of the outer layer 352 are more apparent to the userthan the thinner regions under fluoroscopy.

The transitions in thickness of the outer layer 352 can be preciselycreated at desired locations with automated processes such as grinding,drawing, or forging. Such automated processes eliminate the need forhand measuring and placement of markers and further eliminates the needto bond a separate marker element to other radiolucent sections, thusreducing the manufacturing cost and complexity of the system.

In the present embodiment, the delivery pusher 350 includes three mainindicator regions of the outer layer 352. A proximal region 356 is thelongest of the three at 137 cm, while a middle region 358 is 10 cm and adistal region 360 is 3 cm. The length of each region can be determinedbased on the use of the delivery pusher 350. For example, the 3 cmdistal region 360 may be used during a coil implant procedure, as knownin the art, allowing the user to align the proximal edge of the distalregion 360 with a radiopaque marker on the microcatheter within whichthe delivery pusher 350 is positioned. The diameter of each of theregions depends on the application and size of the implant. For atypical cerebral aneurysm application for example, the proximal region356 may typically measure 0.005-0.015 inches, the middle region 358 maytypically measure 0.001-0.008 inches, while the distal region 360 maytypically measure 0.0005-0.010 inches. The core mandrel 354 willtypically comprise between about 10-80% of the total diameter of thedelivery pusher 350 at any point.

Alternately, the delivery pusher 350 may include any number of differentregions greater than or less than the three shown in FIG. 7.Additionally, the radiopaque material of the core mandrel 354 may onlyextend partially through the delivery pusher 350. For example, theradiopaque material could extend from the proximal end of the coremandrel 354 to three centimeters from the distal end of the deliverypusher 350, providing yet another predetermined position marker visibleunder fluoroscopy.

In this respect, the regions 356, 358, and 360 of delivery pusher 350provide a more precise radiopaque marking system that is easilymanufactured, yet is readily apparent under fluoroscopy. Further, theincreased precision of the markers may decrease complications relatingto improper positioning of the delivery pusher during a procedure.

In operation, the microcatheter is positioned within a patient so that adistal end of the microcatheter is near a target area or lumen. Thedelivery pusher 350 is inserted into the proximal end of themicrocatheter and the core mandrel 354 and outer layer 352 are viewedunder fluoroscopy. The user aligns a radiopaque marker on themicrocatheter with the beginning of the distal region 360, whichcommunicates the location of the implant 112, 302 relative to the tip ofthe microcatheter.

In some situations, for example, small aneurysms where there may be anelevated risk of vessel damage from the stiffness of the delivery pusher350, the user may position the proximal end of the implant slightlywithin the distal end of the microcatheter during detachment. The userthen may push the proximal end of the implant 112, 302 out of themicrocatheter with the next coil, an adjunctive device such asguidewire, or the delivery pusher 102, 202, 301, or 350. In anotherembodiment, the user may use the radiopaque marking system to locate thedistal end of the delivery pusher outside the distal end of themicrocatheter.

Once the implant device 112, 302 of the detachment system 100, 200, or300 is placed in or around the target site, the operator may repeatedlyreposition the implant device 112, 302 as necessary or desired.

When detachment of the implant device 112, 302 at the target site isdesired, the operator applies energy to the heater 106, 206, or 306 byway of the electrical wires 108, 110, 208, 210, 308, or 309. Theelectrical power source for the energy may be any suitable source, suchas, e.g., a wall outlet, a capacitor, a battery, and the like. For oneaspect of this method, electricity with a potential of approximately 1volt to 100 volts is used to generate a current of 1 milliamp to 5000milliamps, depending on the resistance of the detachment system 100,200, or 300.

One embodiment of a connector system 400 that can be used toelectrically couple the detachment system 100, 200, or 300 to the powersource is shown in FIG. 6. The connector system 400 includes anelectrically conductive core mandrel 412 having a proximal endsurrounded by an insulating layer 404. Preferably the insulating layer404 is an insulating sleeve such as a plastic shrink tube of polyolefin,PET, Nylon, PEEK, Teflon, or polyimide. The insulating layer 404 mayalso be a coating such as polyurethane, silicone, Teflon, paralyene. Anelectrically conductive band 406 is disposed on top of the insulatinglayer 404 and secured in place by molding bands 414, adhesive, or epoxy.Thus, the core mandrel 412 and the conductive band 406 are electricallyinsulated from each other. The conductive band 406 is preferablycomposed of any electrically conductive material, such as silver, gold,platinum, steel, copper, conductive polymer, conductive adhesive, orsimilar materials, and can be a band, coil, or foil. Gold is especiallypreferred as the conductive material of the conductive band 406 becauseof the ability of gold to be drawn into a thin wall and its readyavailability. The core mandrel 412 has been previously described and maybe plated with, for example, gold, silver, copper, or aluminum toenhance its electrical conductivity.

The connector system 400 also includes two electrical wires 408 and 410which connect to the conductive band 406 and core member 412,respectively, and to a heating element at the distal end of a deliverysystem such as those described in FIGS. 1, 2, and 4 (not shown in FIG.6). These wires 408 and 410 are preferably connected by soldering,brazing, welding, laser bonding, or conductive adhesive, or similartechniques.

Once the user is ready to release the implant 112, 302 within thepatient, a first electrical clip or connector from a power source isconnected to a non-insulated section 402 of the core mandrel 412 and asecond electrical clip or connector from the power source is connectedto the conductive band 406. Electrical power is applied to the first andsecond electrical clips, forming an electrical circuit within thedetachment system 100, 200, or 300, causing the heater 106, 206, or 306to increase in temperature and sever the tether 104, 310.

Once the detachment system 100, 200, or 300 is connected to the powersource the user may apply a voltage or current as previously described.This causes the heater 106, 206, or 306 to increase in temperature. Whenheated, the pre-tensioned tether 104, 310 will tend to recover to itsunstressed (shorter) length due to heat-induced creep. In this respect,when the tether 104, 310 is heated by the heater 106, 206, or 306; itsoverall size shrinks. However, since each end of the tether 104, 310 isfixed in place as previously described, the tether 104, 310 is unable toshorten in length, ultimately breaking to release the implant device112, 302.

Because there is tension already within the system in the form of aspring 116 or deformation of the tether material 104, 310; the amount ofshrinkage required to break the tether 104, 310 is less than that of asystem without a pre-tensioned tether. Thus, the temperature and timerequired to free the implant device 112, 302 is lower.

FIG. 5 is a graph showing the temperatures at the surface of the PETcover 304 of the detachment system 300. As can be seen, the surfacetemperature of the detachment system 300 during detachment does not varylinearly with time. Specifically, it only takes just under 1 second forthe heat generated by the heating coil 306 to penetrate the insulatingcover 304. After 1 second, the surface temperature of the insulatingcover 304 dramatically increases. Although different outer insulatingmaterial may slightly increase or decrease this 1-second surfacetemperature window, the necessarily small diameter of the detachmentsystem 100, 200, or 300 prevents providing a thick insulating layer thatmay more significantly delay a surface temperature increase.

It should be understood that the embodiments of the detachment system100, 200, or 300 include a variety of possible constructions. Forexample, the insulating cover 304 may be composed of Teflon, PET,polyamide, polyimide, silicone, polyurethane, PEEK, or materials withsimilar characteristics. In the embodiments 100, 200, or 300 the typicalthickness of the insulating cover is 0.0001-0.040 inches. This thicknesswill tend to increase when the device is adapted for use in, forexample, proximal malformations, and decrease when the device is adaptedfor use in more distal, tortuous locations such as, for example,cerebral aneurysms.

In order to minimize the damage and possible complications caused bysuch a surface temperature increase, the present invention detaches theimplant device 112, 302 before the surface temperature begins tosignificantly increase. Preferably, the implant device 112, 302 isdetached in less than a second, and more preferably, in less than 0.75seconds. This prevents the surface temperature from exceeding 50° C.(122° F.), and more preferably, from exceeding 42° C. (107° F.).

Once the user attempts to detach the implant device 112, 302, it isoften necessary to confirm that the detachment has been successful. Thecircuitry integrated into the power source may be used to determinewhether or not the detachment has been successful. In one embodiment ofthe present invention an initial signaling current is provided prior toapplying a detachment current (i.e. current to activate the heater 106,206, or 306 to detach an implant 112, 302). The signaling current isused to determine the inductance in the system before the user attemptsto detach the implant and therefore has a lower value than thedetachment current, so as not to cause premature detachment. After anattempted detachment, a similar signaling current is used to determine asecond inductance value that is compared to the initial inductancevalue. A substantial difference between the initial inductance and thesecond inductance value indicates that the implant 112, 302 hassuccessfully been detached, while the absence of such a differenceindicates unsuccessful detachment. In this respect, the user can easilydetermine if the implant 112, 302 has been detached, even for deliverysystems that utilize nonconductive temperature sensitive polymers toattach an implant, such as those seen in FIGS. 1, 2, and 4.

In the following description and examples, the terms “current” and“electrical current” are used in the most general sense and areunderstood to encompass alternating current (AC), direct current (DC),and radiofrequency current (RF) unless otherwise noted. The term“changing” is defined as any change in current with a frequency abovezero, including both high frequency and low frequency. When a value ismeasured, calculated and/or saved, it is understood that this may bedone either manually or by any known electronic method including, butnot limited to, an electronic circuit, semiconductor, EPROM, computerchip, computer memory such as RAM, ROM, or flash; and the like. Finally,wire windings and toroid shapes carry a broad meaning and include avariety of geometries such as circular, elliptical, spherical,quadrilateral, triangular, and trapezoidal shapes.

When a changing current passes through such objects as wire windings ora toroid, it sets up a magnetic field. As the current increases ordecreases, the magnetic field strength increase or decreases in the sameway. This fluctuation of the magnetic field causes an effect known asinductance, which tends to oppose any further change in current.Inductance (L) in a coil wound around a core is dependant on the numberof turns (N), the cross-sectional area of the core (A), the magneticpermeability of the core (μ), and length of the coil (l) according toequation 1 below:

$\begin{matrix}{L = \frac{{.4}\pi\; N^{2}A\;\mu}{l}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

The heater 106 or 306 is formed from a wound coil with proximal anddistal electrically conductive wires 108, 110, 308, or 309 attached to apower source. The tether 104, 310 has a magnetic permeability μ1 and ispositioned through the center of the resistive heater, having a lengthl, cross sectional area A, and N winds, forming a core as described inthe previous equation. Prior to detachment, a changing signaling currenti1, such as the waveforms shown in FIGS. 3A and 3B, with frequency f1,is sent through the coil windings. This signaling current is generallyinsufficient to detach the implant. Based on the signaling current, theinductive resistance XL (i.e. the electrical resistance due to theinductance within the system) is measured by an electronic circuit suchas an ohmmeter. The initial inductance of the system L1 is thencalculated according to the formula:

$\begin{matrix}{L_{1} = \frac{X_{L}}{2\pi\; f_{1}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

This initial value of the inductance L1 depends on the magneticpermeability μ1 of the core of the tether 104, 310 according to Equation1, and is saved for reference. When detachment is desired, a highercurrent and/or a current with a different frequency than the signalingcurrent is applied through the resistive heater coil, causing the tether104, 310 to release the implant 112, 302 as previously described. Ifdetachment is successful, the tether 104, 310 will no longer be presentwithin the heater 106, 306 and the inside of the heater 106, 306 willfill with another material such as the patient's blood, contrast media,saline solution, or air. This material now within the heater core willhave a magnetic permeability μ2 that is different than the tether coremagnetic permeability μ1.

A second signaling current and frequency f2 is sent through the heater106, 306 and is preferably the same as the first signaling current andfrequency, although one or both may be different without affecting theoperation of the system. Based on the second signaling current, a secondinductance L2 is calculated. If the detachment was successful, thesecond inductance L2 will be different (higher or lower) than the firstinductance L1 due to the difference in the core magnetic permeabilitiesμ1 and μ2. If the detachment was unsuccessful, the inductance valuesshould remain relatively similar (with some tolerance for measurementerror). Once detachment has been confirmed by comparing the differencebetween the two inductances, an alarm or signal can be activated tocommunicate successful detachment to the user. For example, the alarmmight include a beep or an indicator light.

Preferably, the delivery system 100, 300 used according to thisinvention connects to a device that automatically measures inductance atdesired times, performs required calculations, and signals to the userwhen the implant device has detached from the delivery catheter.However, it should be understood that part or all of these steps can bemanually performed to achieve the same result.

The inductance between the attached and detached states can alsopreferably be determined without directly calculating the inductance.For example, the inductive resistance XL can be measured and comparedbefore and after detachment. In another example, the detachment can bedetermined by measuring and comparing the time constant of the system,which is the time required for the current to reach a predeterminedpercentage of its nominal value. Since the time constant depends on theinductance, a change in the time constant would similarly indicate achange in inductance.

The present invention may also include a feedback algorithm that is usedin conjunction with the detachment detection described above. Forexample, the algorithm automatically increases the detachment voltage orcurrent automatically after the prior attempt fails to detach theimplant device. This cycle of measurement, attempted detachment,measurement, and increased detachment voltage/current continues untildetachment is detected or a predetermined current or voltage limit isattained. In this respect, a low power detachment could be firstattempted, followed automatically by increased power or time untildetachment has occurred. Thus, battery life for a mechanism providingthe detachment power is increased while the average coil detachment timeis greatly reduced.

Referring now to FIGS. 9 and 10, there is shown an embodiment of adelivery system 500 for use with the present invention that includes adetachment detection capability. The delivery system 500 operates underthe principle that electrical current passing through a coil held in anexpanded, open gap configuration will encounter more resistance thanelectrical current passing through a coil in a contracted, closed gapconfiguration. In the expanded configuration, the electrical currentmust follow the entire length of the coiled wire. In the contractedconfiguration, the electrical current can bridge the coils and travel ina longitudinal direction.

The delivery system 500 is generally similar to the previously describeddetachment system 300 of the present invention seen in FIG. 4, includinga delivery pusher 301, containing a heater coil 306 that detaches animplant device 302. The detachment system 500 similarly utilizes atether 310 to coupled the implant device 302 to the delivery pusher 301.

The heater coil 306 is preferably a resistance-type heater having aplurality of loops 306A as seen in FIG. 10, that connects to a voltagesource through a connector system at the proximal end of the deliverypusher 301, such as the connector system 400 described in FIG. 6.

The delivery system 500 also includes a heater coil expander 502 thatserves two functions. First, it expands the heater coil 306 such thatthe heater coil 306 maintains a friction-fit attachment to the inside ofthe insulating cover 309, thereby connecting the two. Second, the heatercoil expander 502 expands the heater coil 306 in such a manner thatelectricity is forced to flow around each individual loop 306A of thecoil 306 in order to maximize the resistance of the coil 306.

Maximizing the coil resistance not only serves to heat the coil 306 whenvoltage is passed through, it also sets an initial value (or “normal”value) for the resistance provided by the coil 306, which can be used tocompare a changed resistance state, indicating detachment of the implant302. Hence, the heater coil expander 502 must also be capable ofundergoing change when subjected to heat. In this regard, the heatercoil expander 502 may be made of any suitable sturdy material capable ofholding the heater coil 306 in an expanded, biased state while alsobeing capable of melting or being otherwise reduced by the heat of theheater coil 306 in order to yield to the bias of the heater coil 306 toreturn to an unbiased state. Examples of acceptable materials include,but are not limited to, polymers and monofilament.

The heater coil expander 502 shown in FIGS. 9 and 10 operates bylongitudinally, or radially and longitudinally, expanding a heater coil306 which is normally a closed gap coil in a relaxed state. In otherwords, the individual loops 306A contact each other when the heater coil306 is not stretched or radially expanded. Preferably, the heater coilexpander 502 may have a coiled shape, similar to the heater coil 306 andas seen in FIG. 10. Alternately, the heater coil expander may have acontinuous, tubular shape with helical ridges similar to the individualcoil shapes of the expander 502 in FIG. 10. It should be understood thata variety of different expander shapes that expand the loops or coils306A of the heater coil 306 from each other.

Preferably the power source (previously described in this embodiment andconnected to the connector system 400) also includes a measuringinstrument for measuring the resistance of the heater coil 306. In thisrespect, the power source (preferably located in a hand-sized unit)includes an indicator that communicates when a change in resistance hasoccurred and therefore when detachment of the implant has occurred.

An alternative embodiment of the heater coil expander 512 is shown inFIGS. 10 and 11. The heater coil expander 512 operates in conjunctionwith the heater coil 306 so that the heater loops are in an open gapstate (FIG. 10), and a pusher 350, as previously described in FIG. 7,that conducts electricity. The heater coil 306 is sized to snugly fitaround the pusher 350 in a contracted state. The heater coil expander512 operates to separate the heater coil 306 from the pusher 350,electrically isolating the heater coil 306 therefrom. As the heat fromthe heater coil 306 melts or otherwise reduces or degrades the heatercoil expander 512, the heater coil 306 resumes a contracted state (i.e.,reduced diameter configuration), making electrical, if not physical,contact with the pusher 350 (FIG. 11). In this respect the individualloops are shortened, significantly reducing the resistance of thecircuit and thereby indicating detachment has occurred.

Another alternative embodiment of the present invention, the heater coilexpander 502 may be sized to expand the heater coil 306 against theconductive reinforcement circumference 312 (shown in FIG. 9). Hence,when the coil 306 is in its initial expanded position, the electricallyconductive reinforcement circumference 312 maintains a low initialresistance that is registered by the controller for the circuit (i.e.,the measurement device of the power source).

When the heater coil 306 is energized, the initial resistance is notedand the heater coil expander 306 melts, degrades or otherwise reduces.The heater coil 306 then contracts, releasing the attachment tube 512(and the rest of the implant 510) and the heater coil 306 is no longershorted out by the reinforcement circumference 312. Thus, the circuitexperiences a change in resistance as the electrical current must travelthrough each of the individual loops. This increase in resistancesignifies the implant 302 is detached.

FIGS. 13-16 illustrate another preferred embodiment of a delivery system600 according to the present invention. For illustrative purposes, itshould be noted that the outer body of the system 600 is not shown. Thedelivery system 600 is generally similar to some of the previouslydescribed embodiments, in that it includes a tether 606 that secures animplantable device 612 to the delivery system 600 and a heater coil 604that causes the tether 606 to break, thereby releasing the implantabledevice 612.

However, as seen in these Figures, the heater coil 604 is sized with adiameter that is much smaller than previous embodiments. Morespecifically, the heater coil 604 preferably has an internal passagethat is only slightly larger in diameter than the outer diameter of thetether 606. In other words, the internal diameter of the heater coil 604is substantially the same as the outer diameter of the tether 604.

According to one embodiment, the internal passage of the heating coil604 solely contains the tether 606. According to another embodiment, thediameter of the internal passage may be large enough for only the tether606 to pass through. In another embodiment, the diameter may be largeenough for only the tether and other components, such as support mandrel611 or electrical wires 608 and 610. In either case, at least a portionof the internal diameter of the heater coil 604 maintains a closeproximity to the tether 606, allowing the tether 606 to pass throughonce.

Additionally, the heater coil 604 preferably includes a smaller diameterregion 604A which is positioned closer to the tether 606 than theremaining portions of the coil 604. In this respect, the region 604A canmore efficiently transfer heat to the tether 606 and therefore break thetether with an otherwise lower temperature than without the region 604A.Providing a lower temperature reduces the risk of damaging the patient'stissue surrounding the system 600. In a specific example, the heatercoil 604 has an internal diameter of about 0.007 inch and an internaldiameter of about 0.005 inch at region 604A while the tether 606 has anexternal diameter of about 0.004 inch.

As in previously described embodiments, the heater coil 604 may becomposed of a coiled heating element wire. However, it should beunderstood that other heater configurations are possible, such as asolid, conducting tube or a wire arranged in a non-coiled shape, such asa wave or undulating pattern that forms an overall tubular shape (thatmay not completely surround the tether 606).

Both ends of the tether 606 are preferably secured to an outerstructural coil 602 of the delivery device 600. For example, the ends ofthe tether 606 can be tied, glued (e.g., with U.V. cured adhesive),welded or clamped. It should be understood that the ends of the tether606 can be secured at almost any location along the length of thestructural coil 602, as long as those locations allow at least a portionof the tether 606 to pass through the heater coil 604. For example, bothends of the tether 606 can be secured proximal to the heater coil 604.In another example, one end of the tether can be secured proximal toheater coil 604 and another end can be secured distal to the heater coil604.

As seen in FIGS. 13, 16, and 17, the tether 606 preferably passesthrough openings, cells, loops or other structures of the implantabledevice 612. For example, the tether 606 may pass through cells of astent. As seen in FIG. 16, the tether 606 can pass through multiplecells of the device 612 and is maintained under tension as seen in FIGS.13 and 17. The tension of the tether 606 keeps the device 612 in acompressed state (i.e., compressed in diameter) and abutted to thedistal end of the system 600 (e.g., the distal end of the outer bodymember 609). In this respect, when the tether 606 is broken by theheater coil 604, the tether 606 unwraps from the device 612 and stayswith the delivery system 600, not the device 612. Hence, the tether 606does not remain in the patient to potentially cause unwantedcomplications.

As with previously described embodiments, the delivery system 600 isconnectable to a selectively actuated power supply (e.g., via a buttonon a handle of the delivery device 600). Wires 608 and 610 deliverelectric current to the heater coil 604 at a desired time, causing thecoil 604 to heat and thereby break the tether 606.

Preferably, the heater coil 604 is supported within the delivery system600 by a support mandrel 611 (best seen in FIG. 15) that extends along alength of the system 600. Preferably, the support mandrel 611 is securedto the heater coil 604 by welding, adhesive or a mechanical interlockingarrangement (not shown). The proximal end of the support mandrel 611 ispreferably attached to a core wire or delivery pusher (e.g., pusher 350described in other embodiments in this specification).

The outer coil 602 provides support to the delivery system and can bepositioned on the inside of a lumen of the delivery system body 609 (seeFIG. 17). Alternately, this coil 602 can be positioned between materiallayers of the delivery system body 609 (not shown) or otherwise embeddedin the material of the delivery system body 609.

In operation, a distal end of the delivery system 600 is positioned at atarget location within a patient. When the implantable device 612 (e.g.,catheter, valve or microcoil) has achieved a desired position, the userprovides electric current to the heater coil 604 (e.g., via a button onthe delivery device 600). The heater coil 604, including section 604A,increases in temperature, causing the tether 606 to break. The tether606, previously under tension, passes through the cells or attachmentpoints of the implantable device 612 releasing the device 612 from thedelivery system 600. The delivery system 600 can then be removed fromthe patient, along with the attached tether 606.

It should be understood that other tether arrangements are possibleaccording to the present invention. For example, FIG. 18 illustrates theuse of three tethers 614A, 614B and 614C which attach to differentlocations on the device 612. Preferably, these tethers 614A, 614B and614C have a smaller diameter than the previously described tether 606.In the present preferred embodiment, the tethers 614A, 614B and 614C aretied to the device 612 at knots 616. However, adhesives, clamps andother attachment arrangements are also possible. While not shown in theFigures, each tether 614A, 614B and 614C can be looped through a portionof the device 612, similar to the single tether of previously describedembodiments and attached to a location in the delivery system 600.

Although the invention has been described in terms of particularembodiments and applications, one of ordinary skill in the art, in lightof this teaching, can generate additional embodiments and modificationswithout departing from the spirit of or exceeding the scope of theclaimed invention. For example, the heater coil or heater coil expandercould be constructed to activate a switch that provides a userindication of detachment in some manner. Additionally, a visualindicator may be associated with the change in resistance to provideeasy indication of detachment. Accordingly, it is to be understood thatthe drawings and descriptions herein are proffered by way of example tofacilitate comprehension of the invention and should not be construed tolimit the scope thereof.

What is claimed is:
 1. A delivery system for an implant comprising: anelongated member having a distal end and a proximal end; said distal endof said elongated member operable to hold said implant; a tether memberconnectable to said elongated member and to said implant; and, a heatingmember comprising a resistance-type heater coil that is disposed on saidelongated member; said heating member having a hollow passage in whichat least a portion of said tether member resides; a first electricalwire connected at a distal end of said heater coil and a secondelectrical wire connected at a proximal end of said heater coil, whereinsaid first electrical wire and said second electrical wire supply directcurrent between said distal end of said heater coil and said proximalend of said heater coil; said hollow passage comprising a first regionhaving a first plurality of loops with a first internal diameter and asecond region having a second plurality of loops with a second internaldiameter that is different from said first diameter; wherein said tethermember passes through said first plurality of loops and said secondplurality of loops; and wherein said second diameter is substantiallythe same as an outer diameter of said tether member.
 2. The deliverysystem of claim 1, wherein said tether has an external diameter of about0.004 inch, said first internal diameter is about 0.007 inch and saidsecond internal diameter is about 0.005 inch.
 3. The delivery system ofclaim 1, wherein said heating member is an electrically actuated heatingcoil that is fixed along a side of said elongated member.
 4. Thedelivery system of claim 1, wherein said implant is a stent having aplurality of cells and wherein said tether member is positioned throughat least one of said plurality of cells.
 5. The delivery system of claim4, wherein said tether member passes through multiple cells of saidplurality of cells.
 6. The delivery system of claim 5, wherein saidtether member maintains said stent in a compressed configuration.
 7. Adelivery system for an implant comprising: a pusher member having anelongated shape; a distal end of said pusher member connectable to saidimplant; a tether for connecting said pusher member to said implant; aresistance-type heating element mounted over said tether and suppliedwith direct current, said heating element having a first plurality ofloops with a first internal diameter and a second plurality of loopswith a second internal diameter that is smaller than said first internaldiameter; said tether passing through said first plurality of loops andsaid second plurality of loops; wherein said heating element iscontrollable to generate a temperature increase that causes breakage ofsaid tether.
 8. The delivery system of claim 7, wherein said heatingelement has a tubular shape.
 9. The delivery system of claim 8, whereinsaid second plurality of loops are positioned closer to said tether thansaid first plurality of loops.
 10. The delivery system of claim 9,wherein said tether has an external diameter of about 0.004 inch, saidsecond internal diameter is about 0.007 inch and said first internaldiameter is about 0.005 inch.
 11. The delivery system of claim 7,wherein said tether comprises at least three tether strands and whereineach of said at least three tether strands are fixed to said implant.12. The delivery system of claim 7, wherein said implant is a stenthaving a plurality of cells and wherein said tether is located throughat least some of said plurality of cells.
 13. The delivery system ofclaim 12, wherein said tether maintains said stent in a compressedconfiguration.
 14. An implant delivery system comprising: an elongatedmember sized for insertion into a vascular system of a patient; aresistance-type heater disposed on said elongated member, said heaterhaving an interior passage and a heater length; said heater lengthcomprising a first region having a first internal passage diameterformed from a first plurality of loops and a second region having asecond internal passage diameter formed from a second plurality of loopsthat is different than said first internal passage diameter; a firstelectrical wire connected at a distal end of said heater and a secondelectrical wire connected at a proximal end of said heater; wherein saidfirst electrical wire and said second electrical wire supply directcurrent between said distal end of said heater and said proximal end ofsaid heater; a flexible tether member positioned through said firstregion and said second region of said interior passage of said heater;said flexible tether being connectable to said implant so as to holdsaid implant to said elongated member.
 15. The implant delivery systemof claim 14, wherein said interior passage of said heater is sized toenclose only said tether.
 16. The implant delivery system of claim 14,wherein said tether has an external diameter of about 0.004 inch, saidfirst internal passage diameter is about 0.007 inch, and said secondinternal passage diameter is about 0.005 inch.
 17. The implant deliverysystem of claim 14, wherein an outer surface of said heater is fixed tosaid elongated member.
 18. A delivery system for an implant comprising:an elongated member sized for insertion into a vascular system of apatient; a heater disposed on said elongated member, said heater havingan interior passage, said heater further comprising a first regionhaving a first length formed from a first plurality of loops and a firstinternal passage diameter, and a second region having a second lengthformed from a second plurality of loops and a second internal passagediameter that is different than said first internal passage diameter; afirst electrical wire connected at a distal end of said heater and asecond electrical wire connected at a proximal end of said heater;wherein said first electrical wire and said second electrical wiresupply direct current between said distal end of said heater and saidproximal end of said heater; a plurality of tether members positionedthrough said first length and said second length of said interiorpassage of said heater; said plurality of tether members beingconnectable to said implant so as to hold said implant to said elongatedmember.
 19. The delivery system of claim 18, wherein said plurality oftether members are connectable to a plurality of different locations ofsaid implant.
 20. A method of releasing an implant comprising: providinga delivery device sized for insertion into a vascular system; activatinga resistance-type heater near a distal end of said delivery device wheresaid implant is connected to said delivery device with a tether; saidheater having a passage forming a first portion having a first pluralityof loops and a first internal passage diameter, and a second portionhaving a second plurality of loops and a second internal passagediameter that is different than said first internal passage diameter;said tether positioned through said first portion and said secondportion of said passage; wherein said activating said heater furthercomprises delivering direct current through a first electrical wireconnected at a distal end of said heater and through a second electricalwire connected at a proximal end of said heater; heating said tether bycircumferentially contacting a region of said tether with said firstinternal passage of said heater.
 21. The method of claim 20, whereinsaid first internal passage diameter is smaller than said secondinternal passage diameter.
 22. The method of claim 20, wherein saidtether has an external diameter of about 0.004 inch, said secondinternal passage diameter is about 0.007 inch, and said first internalpassage diameter is about 0.005 inch.